Are no-contact thermometers "totally inaccurate" with "no science" to back them up?

The first time I encountered one of these was last year at the ophthalmologist’s office, a couple of months into the shutdown. I asked if they had ever caught anyone with a fever. The receptionist laughed and said yeah, once, when a fellow had arrived early and had been sitting in his car. She rechecked him after a couple minutes inside, and voila - no more “fever”.

I think the whole thing boils down to “when used correctly” - which I suspect is not the case most of the time.

I feel like most people know when they have a fever, and cancel their appointments.


People claiming that these devices are “totally inaccurate” also have a burden of proof; the null position would be “there is no evidence that these devices are accurate”.

From the cites given above it seems they are accurate enough; or indeed accurate, just not precise.

On the point about skin temperature varying, I don’t think the forehead temperature changes that much as the brain is very sensitive to such changes. If I significantly warmed your forehead with no means of the heat escaping then I’d *induce* a fever.
I have had my temperature taken by IR sensors after running in 35℃ temps and up, covered in sweat, many times. The difference to my forehead skin temperature was minute.

Huh. I would have thought the material dependence would only apply to contact thermos (conduction heating, i think?) where radiative heating would be a pretty pure blackbody spectrum. Interesting.

As far as false pos and false neg, I make too many mistakes translating word problems into math to do the calculations. But a high false pos, low false neg rate would mean you can tell someone is “safe”, while sending home extra people just in case. I think?

We don’t necessarily have to send people home, just follow up with a more accurate reading (eg: with a traditional oral thermometer). A low false negative rate makes for a very good screening measure.


Likely true. The screening process exists not for them, but for other folks who are unaware they have a fever (or don’t care).

I don’t think that’s right. I don’t think that would count as a fever, even if you did heat up some skin. I think a fever is defined in terms of body temperature. The “gold standard” for an accurate core temperature measurement is a rectal thermometer. For obvious reasons, a number of other methods of checking have been implemented and verified as reasonably good ways of determining core temperature. Almost all of them have a different temperature that correlates with the core temperature.

I did research on whether the temporal artery thermometers were accurate after I had kids. I found that they did a ton of research to validate this method as an accurate way to determine core temperature. If I recall correctly, it works specifically because it is measuring at a place where blood comes from the body’s core fairly directly. It can be calibrated to accurately reflect core temperature.

If there is not similar research validating the no contact version, I’d question whether that method has been shown to be a good indication of core temperature as opposed to just local skin temperature. And if it is accurate under lab conditions, I wonder how much people are aware of the specific method required for the reading.

Yeah, I do not currently own a thermometer, relying instead on my realization of “I feel like I have a fever” instead.

You’re right. What I was trying to get at is that there are neurological symptoms of a fever, and you’d get those same symptoms if I artificially kept your forehead hot. It’s not a part of the body that can tolerate large temperature fluctuations.
Vasoconstriction / dilation and sweating are what the body is doing to keep that temperature stable rather than evidence of a spike or fall.

No, IR temperature measurements depend on the emissivity of the material. I’ve used IR temperature measurements thousands of times in industrial settings. Usually in the field where we don’t necessarily know the material, “Is that pipe carbon steel or stainless?” or we don’t want to futz around with changing the settings on our heat gun the easy way to do it is to use spray paint. Lampblack paint has an emissivity of 0.96. Set your gun to 1.0, and you’re good to go, or at least close enough for field work. Actually, every paint regardless of color has an emissivity of 0.96, but around the pulp mill they tend to not go in for a wide spectrum of hues. It’s not a festive environment.

Measuring people’s foreheads would probably benefit from a swipe of paint, but most people don’t like that. The American Society for Testing and Materials (ASTM) says human skin varies from 0.94 to 0.99. Most skin temperature guns are locked in at 0.98 and that’s within the required accuracy.

I’m a little bit confused; isn’t the only difference between one of those Exergen temporal artery thermometers and one of those no-contact thermometers how far away the IR sensor is? Aren’t they both IR thermometers that work exactly the same way?

I mean, the forehead thermometers don’t actually contact your forehead with the sensor; that’s in a little recessed area, and only the rim actually touches you. So the only difference is going to be the distance at which they’re taking the reading, which is more controlled with the forehead ones.

I’m quite confused about this as well


It struck me as extremely odd, as I actually possess both sorts- a Braun forehead thermometer that I bought for last spring’s school year, where the school district required us to take our kids’ temperatures before each school day and record it on a website. I figured a forehead thermometer was far easier, even if it was a bit inaccurate.

I have the pistol-grip kind that I have for my grill/smoker or really anything else that I want to know the temperature of without touching it. Seems to work pretty well too; shooting my kids’ foreheads seems to be within a degree or two of the forehead one.

The one in my dentist’s office is a wall-mounted self-administered type, and it will not register until you’re sufficiently close to it, then it automatically takes a reading and beeps.

I know that at least some of them are totally inaccurate. At one of my workplaces last year, there was a self-serve check-in table where you were supposed to check your temperature. I gave up bothering with it after the gun told me that my temperature was 90.1º, and just went to occasional use of an oral thermometer at home.

Most recently, I saw one that used a full IR camera (there was a display screen above it). That one used facial recognition to tell when there was someone standing in front of it, drew an (accurate) outline of the face to show where it was reading from, and then beeped an OK.

Normal temperature for a person’s skin can vary a lot. If there’s a certain spot that correlates well with core temp, a calibration can be made so that it displays a reasonable approximation of the corresponding core temperature. Or, you’d just have to know what’s normal for that spot. Like normal axillary temperature is between 96.6 and 98°F (usually about 1° lower than oral). So 99° F can be considered a fever if measuring via armpit.

Exergen did the studies to show that the temporal artery location, distance, method etc. with their device provided a good measurement of core body temperature. I don’t know, but I presume there’s also a calibration factor as well, so the Exergen or Braun thermometer doesn’t necessarily display the actual temp. vs the body temp that correlates to what it measures.

A no contact thermometer getting a reading at some distance, on some spot on your head might very accurately report that the surface of your skin is 92° in that spot. It doesn’t mean it isn’t a good thermometer. It does mean it isn’t designed or calibrated for providing core body temperature based on that measurement. And it probably hasn’t been used properly to get that measurement, unless the instructions are clear and were followed.

Exergen may not like this, but temporal artery devices have their share of problems. From the Mayo Clinic:


  • A remote temporal artery thermometer can record a person’s temperature quickly and are easily tolerated.
  • Remote temporal artery thermometers are appropriate for children of any age.

The cons:

  • A temporal artery thermometer may be more expensive than other types of thermometers.
  • This type of thermometer may be less accurate than other types. Direct sunlight, cold temperatures or a sweaty forehead can affect temperature readings. Variations on user technique, such as holding the scanner too far away from the forehead, also may affect accuracy."

Back in high school, when I was getting over having the flu and wanted some downtime for myself before going back to school, I’d just crank up the electric blanket before taking my temperature. Instant fever!

Seems to me that any of these thermometers are accurate enough, given the normal variation in human body temperature.

The ‘normal’ temperature for one specific person can vary as much as 2 degrees F from another person. I normally run about 1ºF low, my sister was .5-1ºF high from 98.6º. And last spring I was in the hospital for 2 weeks, they took my temperature every few hours day & night – and it varied a lot from 3am compared to 3pm.